Power semiconductor devices, such as power metal oxide semiconductor field effect transistors (MOSFETs), have been widely used in power switching devices, such as power supplies, rectifiers, low-voltage motor controllers, or so forth. Power semiconductor devices can be made with a trench topology to improve power density.
In conventional trench type semiconductor devices, as the power density continues to increase, the current that could be made to flow and the power thus generated far exceeds the heat-dissipative capability of the substrate material, such as silicon. As such, the conventional trench type semiconductor devices have shown a propensity for thermal instability and raised concerns for suitability of these devices for linear operation. For instance, forward biased safe operating area (FBSOA) failures can be mainly attributed to localized thermal runaway caused by hot spotting. As an example, when a semiconductor device is operated below the zero temperature coefficient point (ZTCP), if a local region gets hot, the threshold voltage will drop leading to a stronger gate drive and causing the current to rise. This rising current in turn generates more heat in the local region, which further drives down the threshold voltage.
In addition, electrical performance characteristics, such as avalanche ruggedness and electric field crowding, associated with trench type semiconductor devices are also impacted as the power density continues to increase. An avalanche condition can occur when a high voltage is applied across a drain to a source of a trench type semiconductor device. In the avalanche condition, impact ionization of electron-hole pairs can generate avalanche current between a drain of the semiconductor device and a base of the semiconductor device. The avalanche ruggedness of a semiconductor device characterizes the semiconductor device's capability to withstand the avalanche current when subjected to unclamped inductive switching. As dimensions of the trench type semiconductor devices continue to decrease, the electrical performance characteristics, such as avalanche ruggedness and electric field crowding, are also negatively impacted.
Accordingly, there is a need to overcome the drawbacks and deficiencies in the art by providing a semiconductor device with improved thermal stability and electrical performance characteristics.